2015-11-13 08:56:21
Prelude
Prelude
Announcements
- Exam 3 next Friday
Today's topics
- Vision
How vision informs
- What's out there?
- Shape, form, color
- Where is it?
- Position, orientation, motion
Electromagnetic (EM) radiation
Features of EM radiation
- Wavelength/frequency
- Intensity
- Location/position of source
- Reflects off some materials
- Refracted (bent) moving through other materials
EM radiation provides information across space (and time)
Reflectance spectra differ by surface
Optic array specifies geometry of environment
Color == categories of wavelength
- Eyes categorize wavelength into relative intensities within wavelength bands
- RGB ~ Red, Green, Blue
- Long, medium, short wavelengths
- Color is a neural/psychological construct
RGB monitors
How a camera works
The biological camera
The biological camera
Parts of the eye
- Cornea - refraction (2/3 of total)
- Pupil - light intensity; diameter regulated by Iris.
- Lens - refraction (remaining 1/3; focus)
Parts of the eye
- Retina - light detection
- ~ skin or organ of Corti
- Pigment epithelium - regenerate photopigment
- Muscles - move eye, reshape lens, change pupil diameter
Eye forms image on retina
- Image inverted (up/down)
- Image reverseed (left/right)
- Point-to-point map (retinotopic)
- Binocular and monocular zones
Retinal image
Eyes views overlap
The fovea
The fovea
- Central 1-2 deg of visual field
- Aligned with visual axis
- Retinal ganglion cells pushed aside
- Highest acuity vision == best for details
Acuity varies across fovea
Acuity varies across fovea
What part of the skin is like the fovea?
Photoreceptors detect light
Photoreceptors detect light
- Rods
- ~120 M/eye
- Mostly in periphery
- Active in low light conditions
- One wavelength range
Photorceptors detect light
- Cones
- ~5 M/eye
- Mostly in center
- 3 wavelength ranges
Photoreceptors "specialize" in particular wavelengths
How photoreceptors work
- Outer segment
- Membrane disks
- Photopigments
- Inner segment
- Synaptic terminal
- Light hyperpolarizes photoreceptor!
- The dark current
Retina
- Physiologically backwards
- Anatomically inside-out
Retina
- Physiologically backwards
- Dark current
- Anatomically inside-out
- Photoreceptors at back of eye
Retinal layers
Retinal layers
- Bipolar cells
- Horizontal cells
- Retinal ganglion cells
- Amacrine cells
Next time…
- From eye to brain